Inner CR fixed windows vs. opening exterior ones

Hi, following the related threads I have gained a good understanding on the priciples around Control-live room windows. I also have a need for two exterior windows though, and although I understand that the best way to go about it is to not have them at all, in my case it is imperative the main reason being accesibility to the outside A/C units (4th floor on straight - no flat surface wall). This leaves me with the only option to go for commercially available ones. Here in Greece vendors offer the triple-pane & different glass thikness option on "special soundproof" aluminium profiles. They quote a 35db reduction and claim that only one window on the outer concrete wall will be needed (so nothing on the inner plasterboard/rockwool). Too me that sounds like nonsense, so I'd like some advice on this. I fully comprehend the principles that stand for the CR window, i.e. : -mass should be equal to that of wall -every pane of glass is one leaf so gotta have two max. I am worried though on how sufficient a single pane opening window would be in resisting to any kind of weather (yes we do get cold winters) and am generally baffled on which way I should go. One tripled paned? Or two? Or two doubled? or two single? :? As a bonus question, the two windows (2x1,30 m) in question will be in the rear wall of the Control room. Could someone comment on how bad this would be for reflections and acoustics? Many thanks

You have a good grasp of the principles, apparently - two thick, WIDELY separated glasses per window would give the best isolation for sound. When both windows are closed (good seals/tracks are also important, obviously) the wide air space will also help with HEAT insulation. Acoustically, if these are right behind you (and closer than about 10 feet) you may need to build a movable absorber out of 4" (100mm) mineral wool so you don't get reflections off your back window, and use them for mixing... Steve

Thank you Steve